We wish to use chemical modification techniques to study the properties of plastocyanin. We have found that the reaction of plastocyanin with ethylene diamine in the presence of a water-soluble carbodiimide produces four forms of chemically-modified plastocyanin containing 2.1, 3.2, 4.1 and 6.3 molecules of ethylenediamine respectively. All of these forms show a +40mV shift in redox potential. However, the binding constant for the interaction with P700 increases progressively with increasing extents of modification. In the future, we will do the following: (1) We will investigate the reason for the shift in the redox potential by using circular dichroism (CD) and EPR techniques to investigate the environment of the copper and using NMR, CD and fluorescence techniques to investigate possible conformational changes in the molecule. (2) We will attempt to locate the binding site on plastocyanin for both P700 and cytochrome f. To do this, we will study the effect of increasing the extent of modification on P700+ reduction and cytochrome f oxidation. We will also use fluorescence and EPR probes to examine the interactions between these components. (3) We will investigate the binding site for plastocyanin on cytochrome f and Photosystem I using photosensitive bifunctional cross-linking agents. This work will increase our knowledge of electron transport mechanisms and the interactions of electron transport proteins.